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6. INTERPRETING THE DISPLAY
6-3
6.3 Sea Surface Reflections
To reduce sea surface reflections, set the tilt angle to 5° or more so that the
upper edge of the sonar beam does not hit sea surface, or adjust the TVG
functions. When the sonar is used with a narrow tilt angle, the sea surface
reflections cover a large area (up to 300 m to 400 m) as illustrated below.
Sea surface
Sea surface
Tilt angle
indication
Sea surface
reflections
Tilt: 0˚
Tilt: 5-6˚
Sea surface reflections
6.4 Wake
A wake produced by own ship or another ship can be a strong reflecting object
when the sonar is used with a narrow tilt angle. As the wake appears on the
screen as a thick continuous line, it can be easily distinguished from a fish
school. On the other hand, the wake contains a lot of air bubbles which
attenuate ultrasonic energy, making it often difficult to sound beyond the wake.
Own
ship
Other
ship
Wake produced
by other ship
Own ship's
screw noise
Own ship's
screw noise
Own ship's wake
(produced when
own ship turns)
Wake